LOS ANGELES - For Bethany Hamilton, it's all about God and surfing.

That's how it was when a shark ripped off her arm as she lolled on a surfboard off the shores of Kauai in 2003, and that's how it is now as the cinematic version of her story, "Soul Surfer," opens in theaters nationwide.

"He continues to just guide me and lead my every step, because even though the shark attack was scary and crazy, but I think all of this is just as hard to deal with, you know?" says the 21-year-old, who became an instant celebrity after the attack. "Having a movie made about your life -- you've just really got to be on top of it and remember what you are here to do."

What Hamilton is here to do is spread the word about God -- and shred some serious waves.

The youngest in a family of surfers, Hamilton was 13 when she and her best friend, Alana Blanchard, went out with Alana's dad for a surf session on Halloween morning. Hamilton was waiting for waves and dangling her left arm (with its yellow plastic digital watch) into the water when, in a split-second blur of gray, a 14-foot tiger shark lurched from the depths and tore off her arm just below the shoulder.

Alana's quick-thinking father made a tourniquet from a surfboard leash. Hamilton's board, with a big shark bite on one side, became a stretcher. By the time she reached the hospital, she'd lost more than half her blood.

The attack made headlines across the globe. But even more miraculous than her survival was her determination to return to the sport she loved. A month after the attack, she was back out on her surfboard. Six months later, she won fifth place in a national surf competition. Today she is one of the top surfers in the world.

"After the shark attack is when I trusted in God the most," Hamilton says from a Los Angeles hotel suite, where she is promoting "Soul Surfer." "In the movie, they share that one verse: 'For I know the plans that I have for you, says the Lord, plans of peace and not of evil, to give you a future and a hope.' And that was true. Right after the hospital (youth pastor) Sarah (Hill) shared that with me and it just encouraged me to know that God loves me ... and it's inspired me to just keep living and loving and enjoying life."

"Soul Surfer" is based on Hamilton's 2004 book of the same name. While God and Jesus Christ are present on practically every page of Hamilton's book (she dedicates it to "Jesus Christ, my family and the Blanchard family"), faith takes a backseat to surfing in the film.

Director and co-writer Sean McNamara says he aimed to show Hamilton's devotion to Christianity through the character of Sarah Hill, played by singer Carrie Underwood in her big-screen debut.

"When it came time to the religious part of her life, I portrayed a lot of that with her youth minister," McNamara says. "She was going on missions and so forth and I said that will be her part of the story."

Hamilton says she's happy with how her faith comes through in the film, even if it's "maybe not exactly how my personal strength is in Jesus Christ."

"I didn't want it to be preachy. I just wanted it to be natural because that's what it is in my life," she says. "I just hope it will encourage people, whether they believe in God or not, to press on through their hard times and see that good can come out of bad circumstances."

Hamilton also shares her inspirational message through her website, where she blogs about health, surfing and God. She says all people can tap into their own strength and cultivate their own faith.

"Asking God into your heart is basically the first step," she says.

Actress AnnaSophia Robb, who plays Hamilton in the film, says she saw firsthand how the professional surfer relies on her faith, her inner strength and her family to meet the challenges of her life. Her story is about "the tenacity of the human spirit," Robb says.

"She never gave up. She always kept going for it," the actress says. "People can take that whether they are fighting cancer, whether they lose an arm or a limb, or a family member or even a job or anything.

"Bethany is an incredibly special -- it takes a special person to have that strength -- but also she is just a person. She's not a superhero. We all have this strength within ourselves."